fix: write only defined bytes into concurrent Merkle tree changelog - #2389
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CyclicBoundedVec::push copies a ChangelogEntry with ptr::write from a stack value. That copies the undefined value bytes of None nodes and the repr(C) padding between path and index verbatim, so account bytes depended on runtime stack contents. Route all changelog pushes through push_changelog_entry, which zeroes the slot and then writes only the index and the Some nodes. Types and on-chain layout are unchanged. Add tests for the layout the tree relies on (33-byte nodes, entry sizes and index offsets for heights 22/26/32/40) and an end-to-end check that no undefined bytes reach a 0xFF-prefilled buffer.
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Included review availability: Your plan provides up to 2 included reviews per hour; 1 remains after this review. 📝 WalkthroughWalkthroughThe change pins serialized memory layouts and defines written bytes for concurrent Merkle tree changelogs, hash set buckets, and indexed Merkle tree changelog entries. Tests validate sizes, offsets, tags, padding, initialization, state transitions, and buffer-size handling. ChangesSerialized layout and initialization
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: 🔵 Low · up to The PR makes changelog bytes deterministic without changing account layouts or public APIs. It is mergeable with owner awareness that a layout test still appears to inspect potentially uninitialized bytes through transmute, a bounded test-only correctness concern that should be cleaned up. Suggested reviewers: 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
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Inline comments:
In `@program-libs/concurrent-merkle-tree/tests/tests.rs`:
- Around line 3563-3565: Remove the unsafe none_bytes transmute and its tag
assertion from the test near test_changelog_bytes_are_defined; rely on that
existing test to validate the stored None encoding, including the zero tag and
payload.
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program-libs/concurrent-merkle-tree/src/changelog.rsprogram-libs/concurrent-merkle-tree/src/lib.rsprogram-libs/concurrent-merkle-tree/tests/tests.rs
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Transmuting None::<[u8; 32]> to [u8; 33] reads uninitialized payload bytes, which is undefined behavior even if only the tag is asserted.
HashSet wrote `None` and `Some(HashSetCell { sequence_number: None, .. })`
with `ptr::write` / assignment, which leaves the unused enum payload bytes
undefined. In v1 queue accounts those bytes came from the stack, so account
data depended on runtime memory contents.
Write buckets through a `repr(C)` `RawHashSetCell` that defines all 48
bytes. Pin the deployed layout (sizes, offsets and niche tag values) with
compile-time assertions, and reject zero-copy buffers that are missing the
reserved 8-byte gap before the buckets instead of reading past the end.
Pin the v1 indexed changelog entry layout the same way.
Extend the mollusk VAS reproducer with local AMT1, AMT2 and BMT1 cases and
document the harness.
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Superseded by #2392, which contains only the program-libs changes, squashed and rebased on main, plus the CI fix for the dead-code error. |
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Problem
ConcurrentMerkleTreewrites changelog entries into the account buffer viaCyclicBoundedVec::push, which does aptr::writeof aChangelogEntrybuilt on the stack. Two regions of that struct have no defined value on the stack and were copied verbatim into the account:Nonenode inChangelogPath(Option<[u8; 32]>only defines the tag byte forNone), andrepr(C)padding betweenpath(33 * HEIGHTbytes, align 1) andindex: u64(2 bytes at height 22, 6 bytes at height 26).Account bytes therefore depended on runtime stack contents, which is the source of the ok/ok divergence observed when toggling the virtual address space feature (see the
mollusk-vas-repro).Fix
All three changelog pushes (
init,update_leaf_in_tree,append_batch) go through a new privatepush_changelog_entry, which zeroes the slot and then writes onlyindexand theSomenodes.Nonenodes and the padding stay zero.No type, layout, or public API change. Existing accounts remain readable; the only observable difference is that previously undefined bytes are now zero.
A
constassertion pins theOption<[u8; 32]>size the helper relies on.Tests
test_changelog_layout: node is 33 bytes with tag 0/1 at byte 0;ChangelogEntrysizes andindexoffsets for heights 22/26/32/40 (736/872/1064/1328).test_changelog_bytes_are_defined:0xFF-prefilled buffer,init+append_batchat height 10 (6 padding bytes); asserts every node istag == 1or all-zero and the padding is zero.Verified:
cargo test -p light-concurrent-merkle-tree, clippy-D warnings,cargo checkoflight-test-utils/account-compression/light-indexed-merkle-tree/forester, andcargo build-sbfofaccount-compression.Summary by CodeRabbit
Bug Fixes
Tests